This study focuses on a multiproxy analysis of sedimentary records from Lago Bertrand (area 50 km2 ; 227 masl ; 46°55’S 72°50’W) and Lago Thompson (area 1 km2 ; 751 masl ; 45°38’S 72°47’W). Three cores were retrieved during fieldtrips between 2008 and 2011 with an Uwitec gravity corer. For Lago Bertrand, one core was collected in the main lake (LBt09, 102 cm) and another in a lateral extension (LBb11-A, 162 cm). For Lago Thompson, one core was retrieved (LT08-E, 130 cm). Data 210Pb and 137Cs give average sedimentation rates of 1–2 mm/yr for the upper core section from the main part of Lago Bertrand, allowing a decennial resolution. Respectively two and five 14C dates has been obtained for LBt09 and LT08-E. Our aim is to document the climatic variability during the last millennia in Northern Patagonia and its impact on the environment. Lago Bertrand is separated from a pro-glacial lake (Lago Plomo) by a morainic barrier. The sediments of this lake are mainly composed of clayey silts and very few sandy silts. In the cores from the Eastern branch of Lago Bertrand, X-ray radiographies, magnetic susceptibility, Loss On Ignition (LOI) 550℃ and C/N (carbon/nitrogen) ratio profiles evidence well-defined pluri-millimetric laminations with terrestrial organic-rich layers, especially in the central core section. Diatom content is dominated by benthic genera, it does not show major changes except a recent eutrophication of this part of the lake. In the main lake, X-ray radiographies show diffuse pluri-millimetric laminations. The sediments of the main lake appear more homogeneous with less organic-rich layers. They are characterized by low C/N ratio (10), supporting an important aquatic productivity. Inorganic content remains high on the whole core ( 90–95% of the bulk sediment) and biogenic silica profile exhibits two major peaks. We found a same diversity in diatoms than in the lake extension. According to the age model, the changes in aquatic productivity occurred between 1200 BC and 1000 AD. Lago Thompson is characterized by a smaller watershed and less steep sides. Its sediment content is dominated by clayey silts and amorphous particles (essentially diatoms). X-ray radiographies, magnetic susceptibility and LOI 550℃ profiles evidence two tephra deposits at 1410–1440 and 1780–1790 AD. C/N ratio and biogenic silica profiles suggest a bigger productivity during a period equivalent to the Little Ice Age. Diatom assemblage is dominated by planctonic genera (Aulacoseira and Cyclotella) and is less diversified in benthic genera than for Lago Bertrand. Diatoms show specific response to tephra deposits. Planctonic/benthic ratio allow us to identify periods of high and low lake-level matching with moist and dry phases of Little Ice Age (1200–1650 and 1650–1850 AD). Further sedimentological analyses would be undertaken to better characterize the sediment deposition models (sediment core impregnation). In addition, datation of the Lago Bertrand extension core (LBb11-A) would allow us to identify environmental changes found in this study. [less ▲]